r 54 
Campbell . — The Gametophyte and 
The arrangement of the vascular bundles can best be understood from 
a series of cross-sections. Text-fig. 10, A-F, shows several sections from such 
a series from a young sporophyte of about the same age as that shown 
in Text-fig. 8 ; a shows the section passing through the stem apex, x y 
which with the second leaf is surrounded by the sheathing base of the 
cotyledon. The vascular bundle of the latter shows the first tracheides^ 
at the inner limit of the bundle. No tracheary tissue has yet been formed 
in the second leaf. 
In sections taken farther down the two bundles approach, and finally 
Text-fig. io. a-d. Four transverse sections of a young sporophyte showing the coales- 
cence of the leaf-traces to form the axial stele. A passes through the stem apex, st. L 2 youngest leaf. I 
E. The stele, showing the complete coalescence of the xylems of the two leaf-traces. F. Section 
of the root, showing the endodermis and diarch bundle. G. Stem apex, x 270. H. Root- j 
bundle, x 270. 
coalesce. While the two bundles maintain their identity for some time, 
they occupy a pretty well defined oval area, which, however, is not limited 
by a recognizable endodermis. After the coalescence of the bundles is com- 
pleted, and the stele enters the root region, a definite endodermis of the 
typical form is easily seen (f, h). 
Just before the two leaf-traces coalesce, the first tracheary tissue can 
be seen in the trace from the second leaf, and the xylems of the two leaf- 
traces form a continuous band at the junction of the two bundles (e). The 
two leaf-traces are now completely merged into a common ‘ stele ’, which is 
continued downward into the root. It is quite impossible to say where the 
foliar portion of the stele ends and that of the root begins. 
